Thermal relay



Aug. 23, 1932. EL BLETZ 1,873,271

THERMAL RELAY Filed March 12, 1929 wan/[mare aid. 43 W 4; 4/

| 39 Orr may 423-14.

| l 1 I W INVENTOR ATTORNEY Patented Aug. 23, 1932 UNITED STATES PATENTOFFICE EDWARD'BLETZ, OF LEXINGTON, OHIO, ASSIGNOR TO WESTINGHQUSEELECTRIC & MANUFACTURING COMPANY, A CORPORATION OFPENNSYLVANIA THERMALRELAY App1ication filed March 12, 1929. Serial No. 346,393.

My invention relates to circuit-controlling devices and particularly toadjustable thermal relays. r t

An object of my invention is to provide a relatively simple andadjustable thermostaticv switch.

Another object of my invention is to pro vide a snap-acting thermostaticswitch that shall be adjustable, within a predetermined temperaturerange, to vary the temperature while maintaining a substantiallyconstant temperature differential. '1

In practicing my invention, I provide a cupped bimetallic discadjustably held at its central portion on a suitable base provided withcooperating contact members and provided, in addition thereto, with stopmembers for limiting the outward dish of the cupped disc when actuatedfrom its normal position in which the cooperating contact members are inengagement.

. In the single sheet of drawing, 1 Figure 1 is a top plan view of athermal relay embodying my invention, one element thereof being omitted,

Fig. 2 is a view, partially in side eleva tion and partially in radialsection, taken on the line 11-11 of Fig. 1,

Fig. 3 is a View, in side elevation, of the,

assembled device, a part thereof being bro ken away to show the internalconstruction,

Fig. 4 is a schematic view, partially in section and partially in sideelevation, showing one adjustment of the bimetallic disc;

Fig. 5 is a View, similar to Fig. 4. showingI another adjustment of thebimetallic disc, anc I Fig. 6 is a set of curves showing the op erati onof the device embodying my'invention.

A substantially circular base for the device 11 comprises two metaldiscs 12 and 13. The disc 13 is provided with three symmetrically-spacedopenings 14 therethrough which are of double-oval or hour-glass shapeand in which there are located suitably shaped pieces 16 of insulatingmaterial, such as H1103. A substantially circular sheet 17 of mica 18located against the outer surface of sheet 12, and a plurality ofcontact members 18, 19,

21 and 22 are located against the outer surface of the sheet 17.

The cont-act members 18 and 19, are held in their proper operativepositions by two rivets 23. Each of the rivets 23 is provided witharelatively large head 24, as shown more particularly in Fig. 1 of thedrawing, in order that the mica immediately under the head may not bedamaged when the other end is headed over one of the contact members, asshown more particularly in Fig. 2 of the drawing.

Terminal posts 26 and'27 are located in certain of the openings 16 andhave reduced portions extending through the two plates constituting thebase and the mica plate 17 and into the terminal members 21 and 22,respectively, the outer ends of which are headed over, as shown at 28 inFigs. 2 and 3 of the drawing. Small screws 29 are rovided on theterminal posts 26 and 2. to

permit of connecting suitable supply circuit conductors thereto (notshown).

A tubular member 31' is provided with a reduced portion to fit intocentral openings in the plates 12 and 13 and extend slightly beyond theplate of mica 17, the outer end of this portion being headed over, asshown at 32 in Fig.2 of the drawing, in order to hold the two plates 12and 13 and the mica plate 17 in proper operative positions and tightlyagainst one another.

The member 31 is provided with internal I screw threads, as shown at 33,and has a shoulder portion 34 which is of substantially semi-annularextent and is provided for a purpose to be hereinafter set forth indewill move suddenly from one limiting posi- 7 tion to another.

A plurality of contact-bridging members 37 are insulatedly mountedon-the disc near the periphery thereof and are uniformly peripherallyspaced on the disc, the location of the terminal members 18, 19, 21 and22 being such that certain of the spaces between these members will bebridged by the members 37 when the disc is in the position shown in Fig.3 of the drawing. The bridging members 37 are mounted on the disc oninsulated pins 38 on which they have some movement, in order that thebridging members may adapt themselves to different adjustments of thedisc.

Means for supporting the disc adjustably, relatively to the basestructure hereinbefore described, includes a rod 39 having a reduced endportion 41 at one end thereof for fitting loosely into a central openingin the disc 36 to permit the disc to change its shape in accordance withtemperature variations to which the device may be subjected. A nut, orwasher 42 may be located on the portion 41 in order to insure that thematerial of the disc and of the end of the rod 39'shall not be strainedbeyond its permissible limit, either in the assembly or in adjustableoperation of the regaly.

cans for turning the rod 39, which is provided intermediate it ends withexternal screw threads cooperating with the screw threads 33 in themember 31, comprises a handle 43 which may be made ofa molded materialand which has an insert 44 therein of metal having internal recessesextending longitudinally thereof and cooperating with a reduced endportion 46 of the member 39 which is cooperatingly grooved to provideinterfitting portions of the two parts. The end portion 46 is providedwith an axial hole therein which may be screw-threaded to receive thebody of a holding bolt 47 to prevent disengagement of the handle member43 from the rod 39 after assembly thereof.

A cupped bimetallic disc of this kind may have the upper operatingtemperature of the disc, namely, that at which it moves into thelimiting position, substantially as shown in the broken lines of Figs. 4and 5, varied to some degree by varying the position of the centralportion of the disc relatively to the base and the contact membersthereof.

It is not ossible, however, to vary simultaneously th operatingtemperatures with a device of this kind and, in order to obtaintemperatures, I provide a plurality of stop screws 48 which will beoperatively engaged by the periphery of the disc when it has beenactuated to the other of its limiting positions, namely, that one inwhich it is curved away from the base.

When the disc is located relatively to its supporting base, as shown inFig. 4 of the drawing, in which the amount of dish thereof is relativelylarge, it is obvious that a relatively large change of temperature mustoccur before the disc will snap over to the position 49 shown in brokenlines. Let it be assumed that a device of this kind is to operate uponan increaseof temperature and that the disc is cupped a relativelylargeamount initially, and that the amount of this cupping is not reducedappreciably when adjusted to the position shown in Fig. 4 of "thedrawing, it is evident that the increase of temperature necessary beforethe disc will snap over to its other position must be relatively large,that is, the disc will not be operated until the temperature has beenincreased to 'arelatively high value, say, for purposes of illustration,600 F. If it then snaps over to the position shown by the broken linesin Fig. 4, it, and particularly the central portion of it, will belocated relatively close to the plane of the heads of the rigid stopscrews 48 and, therefore, it will be impossible for the reverse disheddisc to have as much dish as it did originally. This means that the stopmembers 48 operate in the same manner as would an initial drop intemperature and this means that only a relatively small reduction intemperature is necessary to cause the disc to snap back to its originalposition. If the disc snap over at a temperature value of approximately600 F., it has been found that, in one type of disc and with a certainadjustment of the stop members 48, the disc will snap back at about 500F. In other words, the disc operates with a temperature differential ofabout 100 F.

Referring now to Fig. 5 of the drawing, the disc 36 is there shown ashaving been drawn downwardly against the base so that it has arelatively small amount of dishing only, and, in line with thestatements made hereinbefore, the disc will now snap over at a muchsmaller temperature increase or at a relatively lower temperature thanset forth in connection with the position shown in Fig. 4 of thedrawing. Let it be assumed that this upper temperature limit is now 400.

Reference to Fig. 5 of the drawing, shows that the reverse dishing ofthe disc is now substantially the same as was shown for the' initialdishing of the disc in Fig. 4 of the drawing and, therefore, it isnecessary that the temperature be reduced to a value much lower than 500F. at which it was found that a disc of this kind would snap back whenin the position shown in Fig. 4 of the drawing. Actualtests have shownthat it is pos- 5 sible to obtain a substantially constant temperaturedifferential between the two operating temperatures of the disc by theadjustment hereinbefore described, in which the stop members 48 areprovided in cooperation with the other elements of the device.

- Reference to Fig. 6 of the drawing may be had, in which curve 51 showsthe upper temperature limits at which a particular disc of this kindwill snap over, that is, move from the position shown by the full linesin Figs. 4 and 5 to that shown by the broken lines in these figures.Curve 52 shows the temperatures at which the discwill snap from theshape shown by the broken lines in Figs. 4 and 5 to its initialposition.

The horizontal base of these curves is indicated as having twenty-fourdivisions, and it has been found possible to obtain a reduction in theupper temperature limits of operation from 600 F. to 400 F. and asimultaneousreduction of the lower temperature limits from 500 F. to 300F. with a total angular motion over twelve of these divisions and thislimit is imposed by a in 53 which is properly located in the mem er 39,in order to engage the arcuate shoulder portion 34 at each end of itstravel. The amount of turning movement of the rod 39 is somewhat lessthan 180 mechanical degrees and trary.

It may be noted that the intermediate portions of curves 51 and 52 aresubstantially straight and extend substantially parallel to each otherand this means that it is possible to obtain a substantially uniformtemperature differential over the desired operating range oftemperatures, as set forth above.

The lower right-hand portion of curve 52 illustrates what happens whenthe stop mem bers 48 are so far away from the base as to be engaged bythe disc 36 either very lightly or not at all. The same holds true withre- 5o 51 which indicates that the disc was so adto go "well beyond thetwelve divisions and, still obtain a variation in the upper and thelengths of the divisions are purely arbi-' gard to the upper left-handportion of curve.

lower temperatures with substantially constant temperature differential.

The device embodying my invention thus provides a thermal relayembodying a snapacting cupped disc, in which means are provided forensuring adjustable operation of the thermostat over a wide range oftemperature values, the temperature differential between the upper andthe lower temperature limits remaining substantially constant. I

A device of this kind permits of operatively associating it with anelectrically heated device and of controllin the energization of theheating unit thereof over a wide range of 7 temperature, whilemaintainin a substantially constant temperature di erential and anelectric flat iron is one device which may be so controlled. Because ofthe variations in the operating conditions of an electric flat iron, atemperature diflferential of F; is not serious, and very successfuloperation of electric irons embodying a device of this kind has beenobtained.

Various modifications may be made in the device embodying my inventionWithout departing from the spirit and scope thereof and I desire,therefore, that only such limitations shall be placed thereon as areimposed by the prior art or are 'set forth in the appended claims.

vI claim as my invention: I l I 1. In a thermally-actuable switch havinga base, contact members thereon, a snap-acting bimetallic disc, andcontact members thereon cooperating with the contact members on the baseto control a circuit, an internally-threadedtubular member secured tothe base at one endthereof and coaxial therewith and having a shoulderportion at its other end, an externally-threaded rod extending throughthe tubular member and having the disc mounted at one of its ends, thescrew threads on the rod and in the tubular member being in engagement,an adjusting lever on the otherend of the rod for turning the same inthe tubular member to adjust the position of the central part of thedisc relatively to the base, and a pin on the rod for engaging theshoulder portion of the tubular member to limit the adjusting movementof the rod and of thedisc.

2. In a thermally actuable switch having a circular base, contactmembers insulatedly fixed thereon at one side thereof, a cuppedbimetallic disc at one side of the base, and contact members thereoncooperating with the contact members on the base, a plurality of stopscrews projecting through the disc adj acentto its periphery and mountedin the base, an internally-threaded tubular member having one endsecured to the base coaxially therewith'and having its other endprovided with a shoulder portion, an externallythreaded rod in saidtubular member having the disc mounted thereon at that end extendingthrough the base to that side having the contact members securedthereto, the internal and external screw threads in the tubular memberand on the rod being in engagement, an adjusting lever on the other endof the rod for turning the same to vary the position of the centralportion of the iso relatively to the base and the outer ends of the stoscrews, and a pin in said rod for engaging t e shoulder portion of thetubular member to limit the turning movement of the rod in eitherdirection of movement.

In testimony whereof, I have hereunto subscribed my name this Fifth dayof March,

EDWARD BLETZ.

